Crossing a previously deployed intravascular stent with a catheter over a guidewire presents a challenge, especially during neurovascular procedures. Often it is not possible to advance a catheter over the guidewire because of a ledge formed between the outer diameter of the guidewire and the outer diameter of the catheter. FIG. 1A illustrates a microcatheter 2 with a guidewire 4, therethrough, hung up on a stent strut 6. FIG. 1A is a forward view of the catheter 2 over the wire 4 crossing through the stent cell 10 and getting caught on the stent struts 6 (as in the case of an aneurysm coiling procedure) because of the difference in diameters of the guidewire 4 and the catheter 2. FIG. 1B illustrates the ledge 8, as the difference between the outer diameter of the guidewire 4 and the outer diameter of the microcatheter 2. The ledge 8 distance can actually be greater as the guidewire 4 can be displaced from a center axis of the microcatheter 2, creating even more of a gap. FIG. 1C illustrates the above problem. The stent cell 10 is placed within a body lumen (not illustrated) and the guidewire 4 is guided through the lumen. The microcatheter 2 is then advanced along the guidewire 4 and gets hung up on the stent strut 6 at the ledge 8.
Prior art attempts to solve this problem included “rounding” or “beveling” the tip of the catheter to facilitate tracking over the struts of the device. Additionally, a multi-catheter configuration has been tried in which catheters of progressively smaller diameters are inserted coaxially inside each other to minimize the ledge.
What is needed is a simple mechanism to prevent the ledge 8 from catching on the stent strut 6 while still being able to advance the guidewire 4 and microcatheter 2.